The present invention relates to a plotting head which is moved relative to a sheet of recording material in a plotting machine to produce a graphic display either directly on the material or on other mediums in subsequent developing or printing processes.
One of the most important characteristics of a plotter is its ability to produce graphic information of uniform, high quality. Quite apart from accuracy, the graphic information should be clear, of high contrast and uniform intensity. With the advent of numerically controlled plotters and higher plotting speeds, the difficulty of maintaining traces of uniform character and high contrast at many different plotting speeds has led to controlled wet ink systems such as disclosed in U.S. Pat. No. 3,781,907, issued Dec. 25, 1973 and entitled APPARATUS AND METHOD FOR EXPRESSING WRITING FLUID FROM A PLOTTING PEN issued to the assignee of the present invention. Plotting heads capable of maintaining high quality line characteristics at all speeds are still being striven for.
It is, accordingly, a general object of the present invention to provide a plotting head which utilizes a slender shaft of consumable marking material such as graphite or pencil lead. Such materials maintain line traces of uniform character and high contrast at various plotting speeds and avoid the complexities and potential blotching of wet ink systems described above.